A turbomachine, in particular a gas turbine engine, may comprise guide vanes in order to direct gas flows generated by the compressor and turbine stages of an engine. These vanes generally act between the stages of the engine to direct and guide the gas flow.
The nozzle guide vane assembly is one of the most difficult areas of design because the vanes sustain the highest temperature in the engine and they must perform an efficient aerodynamic function on the hot gases which flow from the combustion chamber. The gases typically have an entry temperature between 850 and 1700° C. and may reach velocities of over 750 meters per second.
Guide vanes are often made as an annular array of separate vanes, each vane comprising an aerofoil and inner and outer platforms formed integrally with the aerofoil.
In order to maintain a high level of efficiency it is necessary to prevent leakage of the hot gases and this is of particular importance at the circumferential interfaces between the separate vanes which make up the guide vane and at the axial interfaces of the guide vane array with the preceding and following components of the turbomachine.
However, the operating conditions are such that components in the turbomachine exhibit different rates of expansion and contraction. This brings about geometric relationships that change considerably during use, which makes it difficult to seal one section of the turbomachine from another to prevent leakage of gas between the two portions.
As shown in FIG. 1, the guide vane 2 comprises an aerofoil portion 4 and an outer platform 6. The outer platform 6 of the guide vane 2 is coupled at one end to a liner 8. The liner 8 sits radially outside a blade 10. Similarly to the guide vane 2, the liner 8 may be made as an annular array of separate liners, each liner being associated with a corresponding guide vane 2.
The guide vane assembly comprising the guide vane 2 and the liner 8 is coupled to the radially exterior casing components of the turbomachine at one end via the radial projection 12 of the guide vane 2. The radial projection 12 is sandwiched between the casing element 14 and the previous casing element. The radial projection 12 prevents axial displacement of the guide vane 2. However the radial projection need not be load bearing since the aerofoil portion 4 provides structural support for the outer platform 6. In fact, the radial projection 12 is sandwiched between the adjacent casing elements in such a manner that the guide vane may expand radially.
The guide vane assembly is coupled to the radially exterior components of the turbomachine at its other end via the radial projection 16 of the liner 8. Since the liner 8 is not structurally supported, the interface further comprises a liner hanger 18 which projects axially from the casing element 18. The liner hanger 18 is received within a recess 20 in the liner 8 and acts to retain the liner 8 radially.
It is known to couple the guide vane 2 to the liner 8 via a “bird's mouth” interface. In such a bird's mouth interface the liner 8 terminates in a bifurcated jaw 22 for receiving a projection 24 of the outer platform 6 of the guide vane 2. This interface between the guide vane 2 and the liner 8 provides for a certain amount of relative axial displacement between the guide vane 2 and the liner 8. As well as axial displacement, the components also experience relative radial displacement caused by thermal expansion, G-forces and gyroscopic loads. Radial displacement of the guide vane 2, particularly the outer platform 6 of the guide vane 2 caused by expansion of the aerofoil portion 4, relative to the liner 8 causes the bifurcated jaw 22 to be splayed. The splayed jaw 22 thus allows the interface to provide the necessary radial displacement between the components. However the splayed jaw 22 increases the amount of gas leaked through the interface and thus this configuration is not best suited to applications where there is radial displacement between the guide vane 2 and the liner 8 and a high level of hermetical sealing is required.
It is an object of the present invention to provide an improved interface between the guide vane and the liner and to allow for radial displacement without excess leakage through the interface.